Bruce,
I am investigating the APC Infrastructure and Liebert XDH systems for a
new small (1000 sqft).
The benefits seem to outweigh the potential downsides. They include
relatively easy n+1 capacity, tightly coupled cooling for efficiency,
and containment to prevent air mixing. Virginia Tech has been using the
Liebert XDV units as supplemental cooling for System X since it was
installed. I believe that other top 100 installations are planned that
will use the XDH.
Infrastuxture seems to be good on a price for performance basis because
the units are modular and generic.
Mike Davis